Newly-discovered Pandoravirus is largest virus ever found

Scott Sutherland

GeekquinoxJuly 20, 2013

The phrase "giant virus" sounds pretty ominous, but that's what's been discovered dwelling underwater by researchers in France. Named 'Pandoravirus', this monster is the biggest virus ever found, but even with its size and creepy name, is it dangerous to us?

Typical viruses — ones we're used to, like influenza — are really small. Influenza measures about 100 nanometers (nm) across, whereas rabies is a bulkier 180 nm. By comparison, the width of a strand of spider's webbing is about 5000 nanometers wide. Viruses don't have to be big, just big enough to carry their key genetic material. They do their thing by injecting themselves into larger cells and using the cells' own reproductive process to make more viruses.

Now here comes something else entirely, though. This Pandoravirus is 1,000 times bigger than the flu virus. So big, you don't need a fancy high-powered microscope to see it. That's not all that's big about it, either. Our familiar flu virus carries about 13 genes, but Pandoravirus racks up an astonishing 2,556! Even more remarkable is that 94% of those genes are completely unknown to science.

You might be wondering why it took so long to discover, if it's so huge. Among its other mysteries, Pandoravirus doesn't look much like other viruses — aside from the fact it's so large, it's more of a blob that most of its relatives. One of the researchers on the team who made this discovery, Jean-Michel Claverie, had actually received a sample of the virus 10 years ago, but he thought it was simply a mislabeled bacteria. He and his team, including wife Chantal Abergel, uncovered the truth of the matter when they got hints of giant viruses from another recent survey. They then obtained sediment samples to test from both seawater near Chile, and freshwater in Australia.

Speaking to NPR, Cleverie and Abergel related how they removed any bacteria from the samples and then set the virus loose on amoebas in their lab. Abergel told NPR "If they die, we suspect that there's something in there that killed them."

What the team ended up with was evidence of two kinds of pandoraviruses (and, presumably, a lot of dead amoebas).

Apart from being cool for having provided evidence for the 'monster truck' of viruses, this study is exciting to biologists and geneticists alike because, like its namesake Pandora's Box, these pandoraviruses seem to contain not only thousands of unknown genes but, Claverie suspects, they may come from a different origin than other viruses living today.

"We believe that those new pandoraviruses have emerged from a new ancestral cellular type that no longer exists," he told NPR. That particular belief is disputed, but either way there is a lot still to be understood about these genetic oddities.

As they appear to be widespread in bodies of water around the world, Claverie is next looking into what might be their role in the marine ecosystem. But, and here's the answer to the question from the start - can they make us sick. Dr. Claverie is quoted in the New York Times, saying "I don't believe we have the proof at the moment that these viruses could infect humans. But again, never say never."

Well, that's almost reassuring.

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